The invention relates to an apparatus for the analysis of atomic and/or molecular elements by wavelength dispersive X-ray spectrometric devices comprising at least one reflection—or focussing device including a multi-layer structure, particularly an apparatus wherein fluorescence rays generated by a sample to be analyzed when subjected to incident primary X-ray or electron radiation are directed onto a mirror or focussing device before reaching a measuring or analysis detector. The mirror or focussing device is formed by a multi-layer structure comprising layer pairs each including a first layer element formed by carbon or scandium. The invention also resides in an analysis method employing such apparatus.
Apparatus and methods of this type are known for example from DE OS 199 26 056. They are used in scientific analyses but also in industrial applications for the detection of atomic and/or molecular elements in various areas for example when impurities or disturbances present in examples in only small amounts are to be detected or analyzed.
In that case, X-ray or electron beams from any type of X-ray or electron source are directed onto a sample whereby, among others, fluorescence rays are returned from the sample which are induced by the incident X-rays by a well-known physical processes. These fluorescence rays are directed onto a suitable crystal where they are reflected and then directed onto a measuring and analysis arrangement for example in the form of a fluorescence radiation-selective detector. The crystals act as analyzers. These crystals which can be artificial crystals may consist of thin multiple alternate layers of two or more materials with different X-ray optical properties. In connection with the above example, the incident fluorescent rays are reflected from these layers but only that part of the fluorescent rays for which the Bragg equation.nλ=2d sin θis fulfilled,Herein:λ(nm)=1.24/E(keV)
wherein n is a natural number (n=1, 2, 3, 4 . . . )                λ=the wavelength of the x rays, that is,        d=the periodicity (lattice parameter) of the analyzer crystal,        2θ=infraction angle, and        E=energy of the X-rays.        
Taking into consideration the effect of the refraction, which is very small for X-rays, results in an equation which is modified from the first equation whereby from the set angles θ and the lattice parameter d of the analyzer the wavelength of the reflected X-rays can be determined from the first equation or the modification thereof. By varying the angle therefore the wavelength of the reflected rays, that is in the above example the fluorescence rays, can be selected in a controlled manner.
The big advantage of the artificial crystals which consist of regularly changing layers—called in this connection also multi-layer—is that the materials of which the multi-layer consists can be selected and optimized for best results. This is an essential advantage of the manufactured multi-layer as compared to natural crystals.
The intensity of the reflected radiation depends greatly on the materials used for the multi-layer. In addition, the lattice parameters of the multi-layer can be modified within a larger range than it is possible with natural crystals.
It is a particular advantage of the multi-layer analyzer that it facilitates the analysis of light elements with uniform intensity and without health-endangering side effects.
In many cases so far the multi-layer structure or, respectively, the individual layers of the multi-layer structure, have been adapted specifically to the element expected to be analyzed. X-ray fluorescence spectrometers have generally the problem that their effectiveness in the soft X-ray range is insufficient for many examinations. So far multi-layer structures have been used wherein a layer element of a multi-layer pair consisted of vanadium and the other layer element consisted of carbon or wherein the first layer element consisted of iron and the second layer element consisted of scandium. It has been found however, that, with the known multi-layer structures, the yield and the efficiency of X-ray fluorescence spectrometers are very low in the said soft X-ray range. For the scientific and the commercial utilization of the X-ray spectrometers even a small increase of the reflectivity of the multi-layer structure may be essential and commercially of greatest importance.
Another disadvantage of the known X-ray fluorescence spectrometers or, respectively, the multi-layer structures, which are used in this connection, resides in the fact that the known multi-layer structures for the soft X-ray range have a high tendency to interdiffusion and that they are therefore not stable. They are furthermore difficult to manufacture.
It is therefore the object of the present invention to provide an apparatus and method by which the X-ray analysis for detecting carbon and nitrogen can be substantially improved wherein the apparatus and the method can be operated with means essentially known so that conventional analysis apparatus and methods can be utilized essentially unchanged so that relatively little expenses occur with use of the apparatus and method according to the invention.